Recently advanced machines and instruments including semiconductor fabricating equipment, precision machines, measurement/inspection equipment and so on are increasingly envisioned to be compact in construction from many aspects of conserving energy as well as keeping high efficiency benefits. Accordingly, the linear motion guide units incorporated in the relatively sliding parts in a diversity of machines are also needed to be compact in construction and large in load-carrying capacity enough to allow smooth relative sliding movement of a slider along a guide rail. Meanwhile, cylindrical rolling elements rather than balls are preferred for making the liner motion guide unit larger in load-carrying capacity and, among the liner motion guide units using the cylindrical rolling elements or rollers, the slider needs to be compact in construction, especially shorter in length or traveling direction.
In the commonly assigned prior patent document 1 (Japanese Laid-Open Patent Application No. H09-72 335) which will be referred below, there is disclosed the linear motion guide unit in which a carriage in a slider has a return-bore where a sleeve fit to provide a return passage. The sleeve is made to suffer elastic deformation to alleviate the sliding resistance which would be encountered when rolling elements roll through the sleeve, thereby making sure of smooth rolling movement of the rolling elements. With the prior linear motion guide unit constructed as stated earlier, the sleeve fits in the return-bore to provide the return passage extending across the overall length of the return-bore with leaving a circular space between an inside circular wall around the return-bore and an outside circular surface around a radially reduced zone of the sleeve, the circular space being prepared for relieving the elastic deformation of the sleeve. The sleeve is provided in lengthwise direction thereof with a slit and held at fore-and-aft ends thereof to the return-bore, but allowed at the middle zone thereof to alleviate the frictional resistance which would be encountered when rollers roll through the sleeve, thereby making sure of smooth sliding movement of the slider on the guide rail.
In the commonly assigned prior patent document 2 (Japanese Laid-Open Patent Application No. 2006-105 310) there is disclosed a linear motion guide unit in which the return passage is formed with a pipe improved in rigidity or stiffness to make sure of steady application of lubricant around the rolling elements, thereby realizing maintenance-free lubrication. With the linear motion guide unit constructed as stated just earlier, the return passage is defined with a through-hole inside a pipe extending through a lengthwise hole in the carriage. The pipe has windows into which a porous member fits snugly. Lubricant is applied around the rolling elements when the rolling elements roll through the return passage while coming in to engagement with the porous member.
In the commonly assigned prior patent document 3 (Japanese Laid-Open Patent Application No. 2013-92 236) there is disclosed a linear motion guide unit in which a return passage is constituted with a sleeve which fits into a return-bore in a carriage of a slider. With the prior linear motion guide unit made lengthwise short and compact in construction, a cylindrical member to provide the return passage is inserted into a lengthwise bore in the carriage in the slider to make sure of smooth rolling though the return passage. More especially, the cylindrical member to provide the return passage is inserted the lengthwise bore in the carriage with leaving a clearance between them. The cylindrical member has two members susceptible to elastic deformation, one of the members is a bridged beam portion supported at both lengthwise ends thereof and another of the two members is a cantilevered beam portion. Both types of the beam portions are allowed to undergo the elastic deformation under an impact force caused by the rolling elements. The bridged beam portion is born at end support sections formed around the outside peripheries of the cylindrical member and the cantilevered beam portion is fastened or retained at a one end thereof and freed at another end thereof to bend or warp.